The recent demonstration of the efficacy of cholesterol lowering in preventing coronary heart disease highlights the need for better treatments for hypercholesterolemia and atherosclerosis. The dietary approach has been frustrated by inherent biological ineffectiveness as well as poor compliance to dietary regimens by free-living subjects. Recent evidence in animal models and metabolic ward studies indicates that diets low in fat and animal protein and high in plant proteins, carbohydrate and fiber are particularly effective in lowering LDL cholesterol. Long-term studies of patient compliance in an outpatient setting are lacking as are studies of the specificity of these diets for subjects with different hyperlipidemia phenotypes. In a 5 year study of male hyperlipidemic industrial employees we will evaluate compliance and lipid lowering efficacy of two alternative diets low in fat and animal protein and high in plant protein, carbohydrate, and fiber compared to a conventional polyunsaturate supplemented control diet. The two alternative diets differ in the amount of fat restricted and polyunsaturates added both of which may affect the ability of patients to adhere to the diet long term as well as the biologic effect on lipid lowering. Complicance evaluation will be directed at testing patient ability to understand the dietary regimen and incorporate it into his lifestyle. Evaluation instruments will include a 5-day food record and food pattern questionnaires. The goal will be to achieve maximal compliance using behavioral strategies over an initial one year of follow-up. A second year of follow-up will assess the maintenance of dietary modifications without behavioral interventions. Measurements of lipoprotein lipids and apoproteins will present the product of inherent biological efficacy and compliance to the dietary regimen. If subjects can adhere successfully to these lipid lowering diets using techniques developed in this project and can achieve substantial cholesterol lowering, prevention of coronary heart disease using dietary intervention may become a testable reality.